A genetic study of the behavior of repeated genes in the yeast Saccharomyces cerevisiae will be undertaken. The proposed experiments are designed to further study intrachromosomal gene conversion, a genetic exchange that has been proposed to be a mechanism for maintaining the sequence homogeneity observed in repeated genes and to account for immunoglobulin allotypes. Intrachromosomal gene conversion in yeast will be studied genetically by using repeated genes with known genetic markers. This will be accomplished by the techniques of in vitro mutagenesis of a cloned yeast gene and by yeast transformation to form duplications. The genetic behavior and stability of various duplications will be studied by standard genetic tetrad analysis and by a physical analysis of the duplicated genes through Southern hybridization. In addition, another type of genetic exchange between repeated genes, unequal sister chromatid exchange, will be studied both genetically and physically. The conclusions draw from these experiments will have implications for the control and appearance of genetic lesions in repeated genes of higher eukaryotes. Examples are the immunoglobulin and hemoglobin genes. The results of these experiments will also contribute to our understanding of the evolution of repeated genes at a genetic and molecular level.